It is possible to classify current optical fibre cable constructions into two broad categories with reference to the nature of the phenomena induced in the cables. There are so-called "constrained" constructions in which the fibre is embedded in a plastic material whose behaviour has an effect on the transmission medium. There are also "free fibre" constructions which are more frequently found, and which have an alveolar support having well determined characteristics.
In the "constrained" constructions, there are principally two types of cable. The first type comprises an assembly, in layers or groups, of fibres which are reinforced by way of extrusion of one or more sheaths. The second type uses tapes of fibres having maximum compactness, which are assembled into a matrix which is then twisted.
Broadly speaking, three types of "free fibre" construction have been developed. All three types utilise alveolar carries made of plastic material for receiving the fibres and an antitraction/compression/crushing mechanical reinforcement provided by carriers made of metal or synthetic material which are semi-rigid or flexible, or by a combination thereof. These three types will be briefly described below. For more detailed information, see the journal "Commutation et Transmission", 1982,